Color shift direct-view half-tone storage tube



Nov. 29, 1960 2,962,623

COLOR-SHIFT DIRECT-VIEW HALF-TONE STORAGE TUBE Filed Sept. 15, 1959 C.D. BEINTEMA 3 Sheets-Sheet 1 Nov. 29, 1960 c. D. BEINTEMA 2,962,523

COLOR-SHIFT DIRECT-VIEW HALF-TONE STORAGE TUBE Filed Sept. 15, 1959 3Sheets-Sheet 2 wals/mex: @Aurox/; :Para/Muff! 4PM v4 im Nov. 29

C. D. BEINTEMA COLOR-SHIFT DIRECT-VIEW HALF-TONE STORAGE TUBE FiledSept. 15, 1959 3 Sheets-Sheet 5 IMM# MM United States Patent COLOR-SHIFT.DIRECT-VIEW HALF-TONE STORAGE TUBE Chester D. Beintema, Santa Monica,Calif., assigner to Hughes Aircraft Company, Culver City, Calif., acorporation of Delaware Filed Sept. 15, 1959, Ser. No. 840,113

7 Claims. (Cl. 315-12) This invention relates to a direct-view half-tonetype color storage tube and, more particularly, to a direct viewingstorage tube for presenting a display wherein signals of varyingintensity appear in different colors.

In the tube of the present invention, a shift from one color to anotheris employed to indicate a change in the intensity level of the signal.The tube is not of the type generally employed to reproduce a scene incolor in a conventional manner.

In conventional color storage tubes capable of producing a presentationin color, the resolution is limited to the extent that three dots ofphosphor are required for each element of the presentation. Also,because of the mask which is used to control the charging of the storagesurface about the apertures in the storage screen which correspond todifferent colored phosphor dots, the brightness of the presentation issomewhat limited. Further, because it is requisite that differentcolored phosphor dots be printed opposite apertures in the storagescreen which are in all respects similar, it is necessary to use anadditional mask over the storage screen to elect the printing of thedots. This use of an additional mask makes it necessary to limit thediameter of the viewing area and to employ an absolutely flat faceplateon the tube to maintain color purity.

It is an object of this invention to produce a half-tone typedirect-view storage tube wherein variations in signal intensity levelare reproduced in different colors.

Another object of the invention is to provide a directview type storagetube particularly adapted to produce a radar presentation wherein targetecho signals normally appear in a different color from those resultingfrom nolse.

A further object of the invention is to provide a color storage tubecapable of producing a presentation in color which has increasedresolution and brightness over that available in conventional colorstorage tubes.

A still further object of the invention is to provide a color shiftstorage tube having a curved faceplate thus enabling a presentation ofincreased area and brightness to be produced.

The color-shift storage tube of the present invention includes anevacuated envelope for housing the various elements of the tube havingeither a at or curved faceplate on the inner surface of which isdisposed the phosphor configuration which constitutes the viewingscreen. In particular, the viewing screen is made up of phosphor dots ofone color. Each of the phosphor dots is surrounded by one or moreconcentric rings of dilferent colored phosphor. The outer ring abouteach of the dots may overlap with adjacent rings without detrimentaleffect on the operation of the device and thus form a continuoussingle-colored background for the dots and, if more than two colors areused, the inner rings. In addition, a conventional type storage screenis employed having circular apertures of approximately one-half thediameter of the phosphor dots disposed in alignment with the centerportion of each dot. A collector grid, an

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electron writing gun and an electron Hood gun with a suitable lloodelectron collimation system are also employed in a conventional manner.

In operation, the electron writing gun produces a charge pattern on thestorage surface which, in turn, controls the ow of flood electronsthrough the apertures of the storage screen to the viewing screen. Ithas been found that when the charge surrounding an aperture firstbecomes sufliciently positive to allow llood electrons to penetratethrough the aperture to the viewing screen, the electrons are focused onthe center of the corresponding phosphor dot. As the charge surroundingthe aperture -becomes progressively more positive, the ood electrons arefocused over the entire dot. A still more positive charge causes theflood electrons penetrating through the aperture to be focused in theform of a spot which expands in diameter with increasing positive chargeon the storage surface surrounding the aperture. In the event that eachdot of the viewing screen is surrounded by only one ring of a differentcolor, the flood electrons will first excite only the dot and then thedot and the ring as the charge on the storage surface surrounding thecorresponding aperture in the storage screen is progressively increasedin a positive direction. A more distinct transition may be achieved byspacing the rings from the respective dots or inner rings, if any.

The above-mentione-d and other features and objects 0f this inventionand the manner of obtaining them will become more apparent by referenceto the following description taken in conjunction with the accompanyingdrawings, wherein:

Fig. l shows a cross-sectional schematic view of one embodiment of thepresent invention;

Fig. 2 shows an enlarged portion of a phosphor dot viewing screenwherein each dot is surrounded by only one ring which overlaps withadjacent rings together with a cut-away portion of the storage screen;

Fig. 3 shows an enlarged portion of an alternative embodiment of theviewing screen wherein each dot is surrounded by two concentric rings oftwo dilerent colors, the outer rings overlapping with adjacent ringstogether with a cut-away portion of the storage screen;

Fig. 4 shows a cross-sectional view of enlarged portions of thecollector grid, storage screen and viewing screen of the embodiment ofFig. 1; and

Fig. 5 is a characteristic of the relative degrees of brightness of thedifferent colored phosphors for various potentials on the storagesurface.

Referring now to the drawings, Fig. 1 shows a directviewing color-shiftstorage tube in accordance with the present invention. This tubecomprises an evacuated envelope 10 which includes a comparatively largebellshaped section 11 which has an axially aligned neck portion 12 atthe left eXtermity, as viewed in the drawing, for housing an electrongun 14 for producing an electron beam of elemental cross-sectional areaand horizontal and vertical deecting plates 15, 16, respectively, forcontrolling the deflection of the electron beam. The right extremity ofthe bell-shaped portion 11 of evacuated envelope 10, as viewed in thedrawing, has an extension which constitutes an annular metallic flange17 and a face-seal liange 18. The face-seal ange 18 is, in turn, sealedolf by a faceplate 20.

A viewing screen 22, a more detailed description which will behereinafter presented, is disposed on the inner surface ofthe faceplate26,. Adjacent to and co-extensive with this viewing screen 22, there isdisposed in the order named, a storage screen 24 supported about itsperiphery by a ring 25 and a collector grid 26 supported about itsperiphery by a ring 27. The ring 27 includes an annular portion which isof sufficiently small diameter as to be accommodated by the ring 25.

The storage screen 24 comprises a thin sheet of metal 28 composed, forexample, of cupronickel. The metallic sheet 28 is of the order of from 1to 6 mils thick. As shown in Figs. 2 and 3, the cupronickel sheet 28 isprovided with circular apertures 29 which may, for example, have auniform diameter of 1.0 mil. A storage surface is provided by a layer 30of dielectric material disposed over the remaining areas of metallicsheet 28 on the side thereof opposite the viewing screen 22. This layer30 of dielectric material may constitute, for example, a layer ofmagnesium fluoride of the order of 3 microns thick evaporated on oneside of the cupronickel sheet 28. Alternatively, the layer 30 may beconstituted of zinc sulfide which is made and operated in accordancewith the teachings of applications for patent, Serial No. 795,727,entitled Cathode Ray Tube, filed February 26, 1959, by Norman Lehrer,and Serial No. 800,180, entitled Storage Tube, filed March 18, 1959, byNorman H. Lehrer, both of which have been assigned to the same assigneeas is the present case.

Disposed adjacent to and co-extensive with the storage surface side ofstorage screen 24 is collector grid 26. The collector grid may beprovided by either a woven or electro-formed mesh having a pitch ofapproximately 250 meshes per inch. In operation, the metallic sheet 28of storage screen 24 and the collector grid 26 are maintained atpotentials of |10 volts and +120 volts, respectively, by means ofconnections therefrom to intermediate'terminals of a battery 32, thenegative terminal of which is connected to ground. In particular, a lead33 from ring 25 and metallic sheet 28 of storage screen 24 is connectedto the battery 32 through a load resistor 34. This enables the outputfrom a pulse generator 35 to be connected directly to the cupronickelsheet 28. Pulse generator 35 provides pulses having positive excursions,which pulses raise the potential of the storage surface, thus enablingit to be erased by the flood electrons as will be hereinafter explainedin more detail.

As previously specified, neck portion 12 of evacuated envelope houseselectron writing gun 14 together with the horizontal and verticaldeflecting plates 15, 16, respectively. The gun may, of course, bemagnetically deflected equally well in cases where magnetic, rotatingdeflection yokcs would be used, i.e., for a P.P.I. display. The electronwriting gun 14 includes a cathode 37 and an intensity grid 38. Thecathode 37 of gun 14 is maintained at a potential of the order of -3000volts with respect to ground by means of a connection therefrom to thenegative terminal of a battery 40, the positive terminal of which isconnected to ground. Further, the intensity grid 38 of gun 14 ismaintained at a quiescent potential of the order of 75 volts negativewith respect to cathode 37. This is accomplished by means of aconnection from the grid 38 through a load resistor 41 to the negativeterminal of a source of biasing potential 42, the positive terminal ofwhich is referenced to the cathode 37. Means for modulating theintensity of the electron writing beam is provided by a connection froman input terminal 43 through a capacitor 44 across the load resistor 41to the intensity grid 38 of gun 14.

The electron beam produced by electron writing gun 14 is scanned overthe storage screen 24 in the desired manner by means of horizontal andvertical deflection voltages generated by horizontal and verticaldeflection voltage generators 46 and 4S, respectively. The horizontaldeflection signal is applied to the horizontal dellecting plates 15through capacitors S0, 51 across isolating resistors 52, 53. Similarly,the vertical deflection signal is applied to the vertical deflectingplates 16 through capacitors 54, 55 across isolating resistors 56, 57.The horizontal and vertical deflecting plates 15, 16 are maintained at aquiescent potential of the order of 100 volts positive with respect toground by means of connections from the common junctions betweenresistors 52, 53 and 56, 57 to a tap 58 of a potentiometer 59 4 which,in turn, is connected across the terminals of the battery 32. Inaddition to the above, an equipotential region is maintainedintermediate the deflecting plates 15, 16 and the annular flange 17 bymeans of a conductive coating 61 disposed over the inner surface of thebellshaped portion 11 of evacuated envelope 10 throughout this region.This conductive coating 61 may, for example, be composed of Aquadag andis maintained at a potential which may be equal to that of the quiescentpotential applied to deflecting plates 15, 16 by means of a connectiontherefrom to the tap 58 of potentiometer 59.

A ring source of flood electrons is provided by a flood gun 63 disposedconcentrically about the longitudinal axis of the cylindrical portion 12of evacuated envelope 10 at the left extremity of bell-shaped portion11, as viewed in the drawing. Flood gun 63 includes a directly-heatedcircular lament 64, which has a plurality of uniformly spacedconnections, alternate ones of which are connected across the secondarywinding 65 of a filament transformer 66 which provides analternating-current voltage of approximately l volt. The mean potentialof cathode 64 of flood gun 65 is operated at ground potential by meansof a connection from the mid-point of secondary winding 65 to ground.Further, the flood electrons are diffused and collimated over the areaof the storage screen 24 by means of a channel-shaped electrode 67disposed about the circular filament 64 with the open side facing thestorage screen 24. In addition, an annular funnels'haped electrode 68 isdisposed about the periphery of the collector grid 26 and extendstowards the flood gun 63 by a distance which is a function of thediameter of the tube. In any event, it does not overlap the bell-shapedportion 11 of envelope 10. The channel-shaped electrode 67 of flood gun63 and the annular funnel-shaped electrode 68 are maintained at apotential that is slightly positive relative to the potential ofcollector grid 26. This potential may, for example, be of the order ofvolts positive with respect to ground and is effected by means ofconnections from the electrodes 67, 68 to the positive terminal of thebattery 32.

Referring now to Fig. 2, there is shown a plan view of an enlargedportion of the viewing screen 22 which is partially covered by acorrespondingly enlarged portion of the storage screen 24. As previouslyspecified, the storage screen 24 comprises a metallic sheet 28 which isprovided with spaced apertures 29 and covered with a layer 30 ofsecondary electron emissive dielectric material which provides storagesurface. The viewing screen 22 includes phosphor dots 70 which aredisposed in alignment with each of the circular apertures 29 in thestorage screen 24. The phosphor dots 70 are all constituted of a singlecolored phosphor which may, for example, be of a red light emittingtype. These phosphor dots 70 have a diameter which is from 50% to 100%greater than the diameter of the circular apertures 29. Thus. in thecase where the circular apertures 29 are l mil in diameter, the diameterof the phosphor dots will be from 1% to 2 mils in diameter. Surroundingeach of the phosphor dots 70 there is disposed a concentric ring ofdifferent colored phosphor. In the event that the apertures 29 aresufficiently close together to allow the concentric rings to overlap,there will be a continuous layer 72 or background of different coloredphosphor which surrounds all of the phosphor dots 70. This continuouslayer 72 may, for example, be provided by a green light emittingphosphor. Also, if it is desired to have an abrupt transfer from thecolor of the dots 70 to the color of the background layer 72 in theoperation of the tube, the background layer 72 is spaced from thephosphor dots 70. On the other hand, if it is desired to have a gradualtransition from the one color to the other in the operation of the tube,the background layer 72 is juxtaposed to each of the phosphor dots 70.Lastly, a thin film 74 of aluminum is evaporated over the entire area ofthe viewing screen 22.

In fabricating the viewing screen 22, there are several nethods whichcan be `used to print the phosphor dots 70 and the layer 72. First,after positioning the storage screen 24 in front of treated surfacewhere the viewing screen 22 is to be produced, a point source of lightis moved in a circle. The image thus exposed on the photographicallytreated phosphor plate will be a ring, the size of which depends on thegeometry of the printing lighthouse setup. The dots may be exposed bymoving the point source of light along its axis and thus expose thecenter of the rings.

Secondly, an annular light source may be used to print the rings byimaging the annular light source through the storage screen 24. Asbefore, a` point source of light can be used lto print the dots 70.

Also, reverse printing may be used. That is, the dots 70 are printedfirst and then the second phosphor is exposed from the faceplate side.The first set of dots 70 will mask the phosphor behind them and thelight from the faceplate side thus cannot fix the phosphor in these.areas and it will be washed away in the developing process. Thephosphors used and the order of deposition will depend on the ultimateuse of the device.

Referring again to Fig. 1, the aluminum film 74 of viewing screen 22 ismaintained at a potential of the order of 5000 volts positive withrespect to ground. This is accomplished by a metal pin 75 which isinserted through a glass bead 76 which is, in turn, sealed to theperiphery of an aperture through the side wall of the face-seal flange18. The inner surface of the face-seal flange 18 intermediate theviewing screen 22 and the pin75 is insulated by means of a layer 77 offrit which is subsequently fused. A mixture of gold flake and frit isthen painted over layer 77 between the pin 75 and the aluminum film 24of viewing screen 22 and fused thereby to provide an electricalconnection 78 from the pin 75 to the viewing screen 22. The pin 75 isthen connected to the positive `terminal of a battery 79, the negativeterminal of which is connected to ground.

According to the present invention, the operation of the discloseddirect-viewing half-tone storage tube may be similar to that of thehalf-tone storage tube disclosed in Patent No. 2,790,929, entitledDirect-Viewing Half-Tone Storage Device, issued to Elvin E. Herman, etal., on April 30, 1957, which patent is assigned to the same assignee asthe present application. In general, the fiood gun 63 is operated toprovide a uniform collimated flow of low velocity electrons over theentire storage area of storage screen 24. The storage surface of storagescreen 24 is prepared for writing by applying a 5 4to 10 volt positivepulse generated by the pulse generator 35 .to the cupronickel sheet 28of the storage screen "224. Initially the ood electrons will havecharged the storage surface to the potential of the flood gun cathode64, which potential is substantially at ground. yBecause ofthe-,capacitance between the storage surface and the cupron'ickel sheet28, the application of the pulse to the cupronrickel sheet 28 raises thepotential of the storage surface by lan amount which corresponds to theamplitude of the pulse. The flood electrons can then commence chargingthe storage surface towards ground potential. Upon completion of thepulse, the potentials of the storage surface follow the negativeexcursion of the trailing edge of the"` pulse whereby thestorage surfaceultimately assumes aquiescent potential of fromy 5 to 10 volts negativewith respect to ground.

Writing is accomplished by applying a signal to input terminal 43thereby to current modulate the high-energy high-current densityelectron beam produced by the electron writing gun 14. This high-energycurrent-modulated electron beam is caused to scan the storage surface ofthe storage screen 24 by the application of suitable defiection voltagesgenerated by horizontal and vertical voltage generators 46, 48 to thedeflecting plates 15, 16, respectively. As the storage screen 24 isscanned by the high-energy electrn beam, the storag' surface is chargedtowards the mean potential of ood cathode 64 by an amount which is afunction of the input signal impressed on terminal 43. The potential ofthe area of storage surface surrounding a given aperture controls theflow of flood electrons through that aperture and thus controls thebrightness of illumination of the corresponding phosphor dot in themanner hereinafter explained.

Referring to Fig. 4, there is shown a cross-sectional view of enlargedportions of the collector grid 26, the storage screen 24 and the viewingscreen 22 of the ernbodiment of Fig. 1 for the purpose of illustratingthe manner in which the device of the present invention operates. Inparticular, the storage surface about a specific aperture 29a of storagescreen 24 is charged to a potential which is in the range of from 5 to-3.5 volts negative with respect to the potential of cathode 64 of floodgun 63. This particular range will, of course, vary with the size of theaperture and the spacing between the storage screen 24 and the viewingscreen 22. At potential levels within this range for the present device,however, the iiood electrons represented by dashed-lines are just ableto penetrate through the aperture 29a. The effect of the chargesurrounding the aperture 29a produces an electron lens, in effect, whichfocuses the flood electrons directly on the phosphor dot 70 which liesin alignment with the aperture 29a. Under these circumstances, only thered of dot 70 will be excited; hence, no green will be visible. V

In the next case, the storage surface surrounding the specific aperture29b of storage screen 24 is charged positively to a potential within therange of from 3.5 to 1.5 volts relative to the potential flood guncathode 64. Under these circumstances, it has been found that theaperture 29b produces a lens which directs the flood electrons in amanner such that they impinge on the viewing screen 22 in the form of aspot which is slightly larger than the dotv 70. Thus, the dot 70 isenergized to produce red light and the inner peripheral regions ofphosphor layer 72 immediately adjacent the dot 70 are energized toproduce green light. The combination of red and green in this mannerproduces light which appears yellow to the eye.

Lastly, if the storage surface surrounding a specific circular aperture29e of storage screen 24 is charged positively to a potential which isfrom 1.5 to 0 volts negative with respect to the potential of flood guncathode 64, and the green phosphor of layer 72 is more efficient thanthe red phosphor of dots 70, the green light will override the redlight, whereby only green light will be observed. It is thus apparentthat as the storage surface surrounding Ithe apertures 29 of storagescreen 24yis charged in the positive direction from -5 to 0 voltsrelative to the potential of flood gun cathode 64, the colors producedby the flood electrons on the viewing screen 22 are first red, thenyellow and, lastly, green. This change in color with charge on thestorage surface is illustrated by the characteristic 82 shown in Fig.`5. It is to be noted that as the charge on the storage surface becomesmore positive, the brightness also increases in addition to thecolorshift. This is because increasing numbers of electrons penetratethrough apertures which open up sufficiently to shift colors. Referringnow to Fig. 3, there is illustrated an alternative embodiment of theviewing screen 22 within additional different colored concentric rings84 are interposed between the phosphor dots 70 and the background layer72. These additional concentric rings 84 may, for example, be composedof a phosphor which emits blue light. The operation is the same aspreviously described.

What is claimed is:

1. A direct-view storage tube comprising a viewing screen having aplurality of fluorescent dots of a single predetermined light emittingcolor disposed in spaced relationship over the entire area thereof andfluorescent material of a light emitting color different from saidpredetermined light emitting color disposed concentrically about each ofsaid dots; a storage screen disposed adjacent to and coextensive withsaid viewing screen and having apertures in substantial alignment witheach of said dots; means for producing a charge pattern on said storagescreen; and means for directing flood electrons uniformly over saidstorage screen whereby the charge on the storage surface surroundingeach aperture controls the characteristics of the flow of said floodelectrons therethrough to said viewing screen to produce a presentationwherein different potential levels of said charge pattern correspond todifferent colors.

2. A direct-view storage tube comprising a viewing screen having aplurality of fluorescent dots of substantially uniform diameter and of afirst light emitting color disposed in spaced relationship over theentire area thereof and fluorescent material of a second light emittingcolor different from said first light emitting color disposedconcentrically about each of said dots; a storage screen disposedadjacent to and co-extensive with said viewing screen having circularapertures in substantial alignment with each of said dots, the diameterof said circular apertures being no less than the diameter of said dots;means for producing a charge pattern on said storage screen; and meansfor directing flood electrons uniformly over said storage screen wherebythe charge on the storage surface surrounding each aperture controls thecharacteristics of the flow of said ood electrons therethrough to saidviewing screen to prod-ucc a presentation wherein different potentiallevels of said charge pattern correspond to different colors.

3. The directview storage tube as defined in claim 2 wherein saidcircular apertures are all of an equal diameter that is from 50% to 100%greater than the diameter of; said tluorescent dots of substantiallyurlifnrnv diameter.

4. The direct-view storage tube as defined in claim 2 wherein said firstlight emitting color is red and said second light emitting color isgreen.

5. The direct-view storage tube as defined in claim 2 wherein saidfluorescent material of a second light emitting color is disposedimmediately adjacent to said fluorescent dots.

6. The direct-view storage tube as defined in claim 2 wherein saidfluorescent material of a second light emitting color is spacedconcentrically about said fluorescent dots.

7. A direct-view storage tube comprising a viewing screen having aplurality of fluorescent dots of substantially uniform diameter and of afirst light emitting color disposed in spaced relationship over theentire area thereof, a fluorescent material of a second light emittingcolor different from said first light emitting color disposedconcentrically about each of said dots, and fluorescent material of athird light emitting color different from said first and second lightemitting colors disposed over the remaining area of said viewing screen;a storage screen disposed adjacent to and co-extensive with said viewingscreen and having circular apertures in substantial alignment with eachof said dots, the diameter of said circular apertures being no less thanthe diameter of said dots; means for producing a charge pattern on saidstorage screen; and means for directing flood electrons uniformly oversaid storage screen whereby the charge on the storage surfacesurrounding each aperture controls the characteristics of the flow'ofsaid flood electrons therethrough to said viewing screen -to produce apresentation wherein different potential levels of said charge patterncorrespond to different colors.

No references cited.

